Maybe your default connection in XAMPP is utf8?
With this combination:
locale en_US
client_charset utf-8
connection_charset Off
database_charset Off
charset_normalization Off
mysql default connection: latin1
ojs table encodings: utf8
You might end up with a situation where everything seems fine when looking from OJS, but the utf8 characters are actually saved as latin1, like this: Ô ß è
So I would check the server default connection setting first.